During lens development, there is a differential regulation of proteins and polypeptides. In rat, at least one beta crystallin polypeptide and one gamma crystallin are not present at birth but become prominent with age. In the human lens and in the monkey lens, the low moleoular weight proteins also have alterations during aging. One of these low molecular weight proteins in the human lens increases with age but may be lacking in the soluble protein from cataractous zones. Thje monkey lens has been studied with particular reference to these proteins as well as some of the glycolytic enzymes. Glyceraldehyde-3-phosphate dehydrogenase, which decreases in cataract formation, has been isolated. This enzyme has many properties which are similar to the enzyme isolated from rabbit muscle. Work has also been conducted on lens epithelial cells in tissue culture to investigate the influence of a retinoblastoma-derived growth factor on the growth of the cells.